Has anyone out there built both the first Zen amp and the Son of Zen? Can anyone compare them for me? The 1st Zen is impressive. I'm wondering how much better SoZ would sound, so I can justify another project.

I wasn't happy with the comments Mr. Pass made in the project description.

I don't think he liked the design. He just made it to satisfy a portion of the population that wanted super-simplicity and more power.

The problems with more THD and more power disapation turned me off.

Also, I think you were in the conversation about the matched MOSFETs. I never found a way to get them. The only way to do it was add resistors in the network to balance them. These resistors are expensive. They have to handle a lot of power.

Well, I don't know exactly how to reply to that, but I will say there has to be something to the design of SoZ because of the shear fact that I don't think he would have put it out JUST to satisfy the readers. He wouldn't have waited 3 years to put it out in A.E. There's some thought behind it. It is completely different from the original Zen amp in many ways.

And, there are several beautifully executed SoZ on the Pass site. Some saying that SoZ holds it own against other well known high end designs. That right there should be enough for me to go a make this amp.

What bothers me is the waste (in heat) that it creates. I emailed Mr. Pass several years ago when the article first came out, asking whether or not I could replace the power resistors with a constant-current source. He said it was possible. By replacing one side w/ a constant-current source, you could save more 20% in dissipation, I believe he said.

If I knew exactly how to do that, I would built it tomorrow. But I don't. If anyone out there reads this and knows how to do it, let me know!!

I know what you mean though. When I first saw the schematic for it, I thought it was too good to be true! It was. It gained may good traits, but lost in the heat dissipation department. You can't please everybody!

Pass lab's web site provides service manual of some Aleph amps for downloads. The manual contains the complete circuit of the amp. I checked the Aleph 3 circuit which Pass said that it was a single-ended design. The Aleph 3 has 2 gain stages but the first gain stage is a differential amp (rather than the single-ended Bride of Zon topology), and the output stage looks like 2 parallel Zen amps (for high current, I guess). So I think Zen design is not meant to be unreal, but it's not meant to be the final answer either. DIYer should modify the circuit as they see appropriate.
I quite think that SOZ is a raw form of the Super Symmetric topology which Pass owns the patent and implements it in his X series amp. No service manual is available at this time though.
If you believe in what Pass quotes, he said of SOZ as "has a wonderful sound, very direct and clear, without the electronic veil imposed be complex feeback circuits." And he also quotes the Balanced Line stage circuit as "This is a particularly good sounding circuit, and I think it sounds significantly better than the Bride of Zen, ..."
I'll be making both soon, but modified as headphone amps.

I agree. It's not a final answer. The Zen project opened up some thought and even pissed some people off enough to try to out do the Zen amp, like the Death of Zen project. It's funny, when I read that article, this guy did everything he could to out do the Zen design, but just kept runnning into walls with the Bi-Polar design. In the end, I don't think he really proved anything. It was more complicated; I think he missed the point. But, I give Rod Elliot credit, because I couldn' design something from nothing. (Except for speakers.)

I once heard a 4-chassis Krell amp system. They were connected to a pair of 6 foot tall DunTech(sp?) speakers. I have never heard anything like that in my life. I've also listened to intergrated, receivers, some tube and bipolar amps. But nothing I have ever heard can claim to be as inexpensive, simple and still sound so damn good.
All I would like is to find someone who's heard Zen and SoZ and for them to give me a description of the two.